1. Field of the Invention
The invention relates to a pressure regulating device, and more particularly to a pressure regulating device that regulates pressure of fuel supplied to a fuel-consuming unit.
2. Description of the Related Art
In a fuel supply system of an internal combustion engine installed on a vehicle or the like, fuel is generally supplied to fuel injectors from a fuel pump and the pressure of fuel in the fuel supply passage is regulated by a pressure regulator which is a pressure regulating device. The interior of the pressure regulating device housing is compartmentalized by a diaphragm into a pressure regulating chamber and a back pressure chamber. In the pressure regulating device, an impelling force in the valve opening direction that is created by a fuel pressure inside the pressure regulating chamber and an impelling force in the valve closing direction from a back pressure chamber side act upon the diaphragm, and then, part of the fuel inside the pressure regulating chamber is discharged according to the displacement of the diaphragm. Thus, the fuel pressure inside the pressure regulating chamber is regulated to a predetermined set pressure based on the impelling force from the back pressure chamber.
An example of a pressure regulating device of this type is available that includes, first and second diaphragms that compartmentalize the housing interior into three pressure chambers, a valve body that is mounted on the first diaphragm so as to open and close a discharge port for pressure regulation inside the first pressure chamber between the housing and the first diaphragm, a pressure receiving body that is connected to the valve body by a connecting rod, which is disposed in the second pressure chamber between the first and second diaphragms, and is fixedly attached to the second diaphragm, and a spring that is provided in the third pressure chamber between the housing and the second diaphragm and impels the pressure receiving body in the valve opening direction. In such pressure regulating device, the fuel pressure that is to be regulated is switched in a plurality of slevels by controlling the pressure supplied to the second and third pressure chambers (see, for example, Japanese Patent Application Publication No. 2009-108684 (JP-A-2009-108684)).
Further, an another example of the pressure regulating device is available, that includes a spring that imparts a back pressure to biases a back surface portion of a valve member at its distal end side, and a plunger that displaces a proximal end portion of the spring when a back pressure fluid is supplied is that imparts a back pressure and biases a back surface portion of a valve member at a distal end side and that is provided at a proximal end side of the spring. The pressure regulating device is configured to switch a set value of the regulated pressure between a low-pressure value and a high-pressure value by switching a pressing load of the spring (see, for example, Japanese Patent Application Publication No. 2009-144686 (JP-A-2009-144686)).
An another example of the pressure regulating device is also available in which an electromagnetic valve functioning as a cut-off valve is mounted on the return pipe of a back pressure chamber that introduces a back pressure fluid, and when it is determined that fuel vapor may be generated, the pressure on the back pressure chamber side is raised to increase the pressure supplying the fuel to the injector to a level at which the generation of fuel vapor is inhibited. In the pressure regulating device, the idling rotation speed is prevented from becoming unstable as a result of fuel vapor generation when the engine is restarted at a high temperature (see, for example, Japanese Patent Application Publication No. 2007-218222 (JP-A-2007-218222)).
However, in the conventional pressure regulating device in which a plunger or second diaphragm is provided at the back pressure chamber side, the interior of the housing is compartmentalized into the first to third pressure chambers that are mutually adjacent in the diaphragm displacement direction. Therefore, the pressure regulating device is difficult to reduce in size and difficult to install. Another problem is that since fluid inlet and outlet are required for each of the first to third pressure chambers, the piping configuration becomes extremely complex.
Further, in the conventional pressure regulating device in which a fluid pressure is introduced into the back pressure chamber inside the housing, the fluid pressure is necessary even outside the pressure regulating chamber when high-pressure regulation is performed. As a result, the excess fluid is necessary, the number of locations where sealing performance is required is increased, and cost is raised.
Further, in the conventional pressure regulating device in which an electromagnetic valve is mounted on the return pipe for returning excess fuel into the fuel tank after the fuel has passed through the fuel gallery, the fuel passage range in which fuel pressure rises when the engine is started becomes wide. The resultant problem is that sealing capable of withstand a high pressure is required for the entire range of fuel passage and therefore the cost of the pressure regulating device is increased.